Mixed-modulation laser

Abstract

To optimize frequency response characteristics more easily by suppressing frequency fluctuations of output modulation light.SOLUTION: Light output from a laser part 101 is demultiplexed by a multiplexing / demultiplexing structure 103 to a first modulation light guide 102a and a second modulation light guide 102b, and propagated in the first modulation light guide 102a and second modulation light guide 102b to be modulated respectively. The light propagated in the first modulation light guide 102a and second modulation light guide 102b is reflected by a reflection part 104 on an element end face, input to the multiplexing / demultiplexing structure 103, and fed back to the light guides by active layers of the laser part 101.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mixed modulation laser.

Background Art

[0002] Direct modulation semiconductor lasers are indispensable light source devices as low-cost high-speed optical signal generators used in data centers and the like where processing ultra-large capacity optical signals has become essential with the explosive development of internet technology. Since the response bandwidth of a direct modulation semiconductor laser is limited by its relaxation oscillation frequency, an increase in the response bandwidth is required for higher speed. Relaxation oscillation frequency f r is expressed by the following equation using the gain constant A of the semiconductor laser g , the carrier lifetime τ s , and the photon lifetime τ p .

[0003]

Formula

[0004] For this reason, to improve the response speed of semiconductor lasers, the focus has been on increasing the gain constant by improving the material constituting the active layer and reducing the photon lifetime by shortening the resonator length. However, since the gain constant is a physical property constant, dramatic improvement is difficult, and shortening the resonator length is limited by the problem of element heat generation, so its response bandwidth has remained at about 40 GHz (Non-Patent Document 1).

[0005] As a technique to overcome the bandwidth limitations imposed by the relaxation oscillation frequencies mentioned above, lasers utilizing the photon-photon resonance phenomenon (Photon-Photon Resonance; PPR) have been proposed (Non-Patent Literature 2, Non-Patent Literature 3). This laser uses an external resonator attached to a semiconductor laser, and by applying PPR between the feedback light from the external resonator (with a given delay time) and the laser oscillation light, a second resonant sensitivity improvement region appears in the response characteristics, thereby achieving bandwidth expansion. There are reports of achieving a 3dB bandwidth of 108GHz using this technique (Non-Patent Literature 4).

[0006] In the high-speed direct-modulation laser using the photon resonance effect described above, the response sensitivity of the semiconductor laser during direct modulation decreases sharply inversely proportional to the square of the modulation frequency in the high-modulation frequency region, as shown in Figure 9 (Figure 9). Therefore, setting the second resonance-like sensitivity improvement region due to the photon resonance effect to the low-modulation frequency region can contribute to bandwidth expansion (shown by the dashed line in Figure 10; the arrows in the figure represent the amount of bandwidth expansion). However, if this is set to the high-modulation frequency region, a region occurs in the intermediate frequency region where the response sensitivity deteriorates below the value where the normalized sensitivity, shown by the thin dotted line, is -3dB (shown by the solid line in Figure 10), and sufficient bandwidth expansion cannot be achieved.

[0007] As a technology to solve this problem, a mixed-modulation laser comprising a laser region 331 and a modulation region 332 has been proposed, as shown in Figure 11 (Non-Patent Literature 5). In this mixed-modulation laser, the laser region 331 and the modulation region 332 are formed on a substrate 301 made of, for example, an n-type compound semiconductor, and the laser region 331 is equipped with an active layer 302 for the laser and oscillates at a single wavelength by a diffraction grating 303 formed in a resonator.

[0008] The modulation region 332 includes an active layer 304 for optical loss modulation. A semiconductor layer 305 made of a p-type compound semiconductor is formed on the active layers 302 and 304, and electrodes 308 and 309 are formed in the laser region 331 and the modulation region 332, respectively. A reflective film 306 is formed on the end face of the modulation region 332, making the modulation region 332 an external resonator. Simultaneously with the modulation of the injection current into the active layer 302, the injection current into the active layer 304 of the modulation region 332, which also acts as an external resonator, is modulated, thereby modulating the optical loss in the modulation region 332.

[0009] In modulation in modulation region 332, the degradation of response sensitivity in the high modulation frequency region is inversely proportional to the modulation frequency, and the degradation is less than that of a typical semiconductor laser response characteristic. For this reason, in the mixed modulation laser of Non-Patent Literature 5, the response characteristics can be made to gradually decrease in the high modulation frequency region as shown by the solid line in Figure 12, and bandwidth expansion can be achieved (arrows shown in Figure 12). In this mixed modulation laser, since modulation region 332 also acts as an external resonator structure, a second resonant sensitivity improvement region due to the photon resonance effect can be made to appear. By introducing this laser configuration, an ultrafast, directly modulated semiconductor laser can be realized that has response characteristics as shown by the solid line in Figure 13 and achieves bandwidth expansion as indicated by the arrows. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] K. Nakahara et al., "112-Gb / s PAM-4 Uncooled (25°C to 85°C) Directly Modulation of 1.3-μm InGaAlAs-MQW DFB BH Lasers with Record High Bandwidth", 45th European Conference on Optical Communication , DOI: 10.1049 / cp.2019.1025, ISBN:978-1-83953-185-9, 2019. [Non-Patent Document 2] M. Radziunas et al., "Improving the Modulation Bandwidth in Semiconductor Lasers by Passive Feedback", IEEE Journal of Selected Topics in Quantum Electronics, vol. 13, no. 1, pp. 136-142, 2007. [Non-Patent Document 3] T. Uusitalo et al., "Analysis of the photon-photon resonance influence on the direct modulation bandwidth of dual-longitudinal-mode distributed feedback lasers", Optical and Quantum Electronics volume, vol. 49, Article number: 46, 2017. [Non-Patent Document 4] S. Yamaoka et al., "239.3-Gbit / s NET RATE PAM-4 TRANSMISSION USING DIRECTLY MODULATED MEMBRANE LASERS ON HIGH-THERMAL-CONDUCTIVITY SiC", 45th European Conference on Optical Communication, DOI: 10.1049 / cp.2019.1022, ISBN:978-1-83953-185-9, 2019. [Non-Patent Document 5] M. Kanno et al., "Measurement of Intrinsic Modulation Bandwidth of Hybrid Modulation Laser", IEEE Photonics Technology Letters, vol. 32, no. 13, pp. 839-842, 2020. [Overview of the project] [Problems that the invention aims to solve]

[0011] Incidentally, the mixed-modulation laser shown in Non-Patent Document 5 uses optical loss modulation by an electric field absorption optical waveguide, where the modulation region is lengthened by applying a reverse bias voltage (Franz-Keldisch effect or quantum confinement Stark effect). Therefore, by applying a reverse bias voltage, the optical loss can be increased to reduce the transmitted light intensity, as shown in Figure 14.

[0012] However, as shown in Figure 15, applying a reverse bias voltage changes the chirp parameter simultaneously with the optical loss. The chirp parameter (α) is a parameter that links the optical intensity and phase fluctuation, and the phase fluctuation amount Δφ is expressed as Δφ = α·ΔI / (2I) using the optical intensity I and the optical intensity fluctuation amount ΔI. Therefore, when the optical loss in the modulation region is modulated, the phase also changes simultaneously through the intensity fluctuation, affecting the frequency fluctuation of the output modulated light and significantly impacting the transmission characteristics of the optical fiber through which the laser light of the mixed-modulation laser propagates.

[0013] Furthermore, as shown in Figure 16, the phase difference (Δφ) between the feedback light from the modulation region and the oscillation light in the laser region affects the frequency response characteristics of the mixed-modulation laser. Therefore, it is necessary to control the phase of the feedback light to an optimal state. However, in the mixed-modulation laser described in Non-Patent Document 5, there is no phase adjustment region, and it was necessary to adjust the laser tip temperature, injection current amount, and bias voltage to the modulation region to achieve optimal operating conditions. However, since the bias voltage also affects the frequency response characteristics, the adjustment was complicated.

[0014] This invention was made to solve the above-mentioned problems, and aims to suppress frequency fluctuations in the output modulated light, thereby making it easier to optimize the frequency response characteristics. [Means for solving the problem]

[0015] The hybrid modulation laser according to the present invention includes: a laser unit composed of a distributed feedback laser having an optical waveguide structure; a first modulated optical waveguide in which optical loss is modulated and refractive index is modulated by modulation of an injected current; a second modulated optical waveguide in which optical loss is modulated and refractive index is modulated by modulation of an injected current; a multiplexing / demultiplexing structure that splits the optical output from the laser unit into the first modulated optical waveguide and the second modulated optical waveguide, and multiplexes the optical output from the first modulated optical waveguide to the laser unit and the optical output from the second modulated optical waveguide to the laser unit; and reflecting units provided at end portions of the first modulated optical waveguide and the second modulated optical waveguide. [Advantageous Effects of Invention]

[0016] According to the present invention, the optical output from the laser unit is split into the first modulated optical waveguide and the second modulated optical waveguide, and the optical output from the first modulated optical waveguide to the laser unit and the optical output from the second modulated optical waveguide to the laser unit are multiplexed, so that frequency fluctuation of the output modulated light can be suppressed, and optimization of frequency response characteristics can be achieved more easily. [Brief Description of Drawings]

[0017] [Figure 1] FIG. 1 is a configuration diagram showing the configuration of a hybrid modulation laser according to Embodiment 1 of the present invention. [Figure 2] FIG. 2 is a distribution diagram showing the distribution of light propagating through a multi-mode interference optical multiplexer / demultiplexer that constitutes the multiplexing / demultiplexing structure 103. [Figure 3] FIG. 3 is a characteristic diagram showing normalized optical loss when the propagation constant of the first modulated optical waveguide 102a changes by Δβ and the propagation constant of the second modulated optical waveguide 102b changes by -Δβ. [Figure 4] FIG. 4 is a characteristic diagram showing changes in the intensity of feedback light to the laser unit 101 and the chirp parameter when the propagation constant of the first modulated optical waveguide 102a is changed by βu=β+(1+δ)·Δβ / 2, and the propagation constant of the phase control optical waveguide of the second modulated optical waveguide 102b is changed by βl=β-(1-δ)·Δβ / 2. [Figure 5] FIG. 5 is a characteristic diagram showing the frequency response characteristics of the hybrid modulation laser 100. [Figure 6]Figure 6 is a characteristic diagram showing the eye waveform of the mixed-modulation laser 100 when operating with a 100 Gb / s NRZ signal. [Figure 7] Figure 7 is a configuration diagram showing the configuration of a mixed-modulation laser according to Embodiment 2 of the present invention. [Figure 8] Figure 8 is a configuration diagram showing the configuration of a mixed-modulation laser according to Embodiment 3 of the present invention. [Figure 9] Figure 9 is a characteristic diagram showing the frequency response characteristics of a typical direct-modulation semiconductor laser. [Figure 10] Figure 10 is a characteristic diagram showing the frequency response characteristics of a semiconductor laser using the photon resonance effect. [Figure 11] Figure 11 is a diagram showing the configuration of a conventional mixed-modulation laser. [Figure 12] Figure 12 is a characteristic diagram showing the frequency response characteristics of a conventional mixed-modulation laser. [Figure 13] Figure 13 is a characteristic diagram showing the frequency response characteristics of a conventional mixed-modulation laser. [Figure 14] Figure 14 is a characteristic diagram showing the reverse bias voltage dependence of the transmitted light output intensity in the modulation region of a conventional mixed-modulation laser using an electric field absorption optical waveguide. [Figure 15] Figure 15 is a characteristic diagram showing the reverse bias voltage dependence of the chirp parameters in the modulation region of a conventional mixed-modulation laser using an electric field absorption optical waveguide. [Figure 16] Figure 16 is a characteristic diagram showing the relationship between the bias voltage to the modulation region and the phase difference Δφ between the feedback light from the modulation region and the oscillating light in the laser region in a conventional mixed-modulation laser. [Modes for carrying out the invention]

[0018] The following describes a mixed-modulation laser according to an embodiment of the present invention.

[0019] [Embodiment 1] First, a mixed-modulation laser 100 according to Embodiment 1 of the present invention will be described with reference to Figure 1. Figure 1 schematically shows a plan view of the mixed-modulation laser 100. The mixed-modulation laser 100 comprises a laser unit 101, a first modulating optical waveguide 102a, a second modulating optical waveguide 102b, and a multiplexing / demultiplexing structure 103. The laser unit 101, the first modulating optical waveguide 102a, the second modulating optical waveguide 102b, and the multiplexing / demultiplexing structure 103 can be monolithically integrated on the same substrate.

[0020] The laser unit 101 is a distributed feedback laser equipped with a waveguide structure, and oscillates at a single wavelength using a diffraction grating 121 formed in a resonator. The laser unit 101 is modulated by a modulation current injected by the first electrode 111.

[0021] The laser unit 101 has an optical waveguide structure with an active layer formed on a substrate as its core, and a diffraction grating 121 is formed in the region where the active layer is formed. The active layer constituting the laser unit 101 can be a multiple quantum well structure made of quantum well layers of InGaAlAs with a band edge wavelength of 1.55 μm. This multiple quantum well structure can consist of five quantum well layers. The laser unit 101 has a waveguide length of 150 μm, and the width of the active layer (core width) can be 1.5 μm.

[0022] In the first modulated optical waveguide 102a, the optical loss and refractive index are modulated by the modulation of the current injected by the second electrode 112a. Similarly, in the second modulated optical waveguide 102b, the optical loss and refractive index are modulated by the modulation of the current injected by the third electrode 112b. Each of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b can have a waveguide length of 150 μm and a core width of 1.5 μm. The refractive index of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b is controlled through the electro-optic (Pockels) effect by applying a reverse bias voltage via the second electrode 112a and the third electrode 112b.

[0023] The multiplexing / demultiplexing structure 103 splits the optical output from the laser unit 101 into a first modulated optical waveguide 102a and a second modulated optical waveguide 102b, and then combines the optical output from the first modulated optical waveguide 102a to the laser unit 101 and the optical output from the second modulated optical waveguide 102b to the laser unit 101. The multiplexing / demultiplexing structure 103 can be configured, for example, from a multimode interferometer optical multiplexer / demultiplexer (Figure 2).

[0024] The multimode interferometric optical multiplexer / demultiplexer constituting the multiplexer / demultiplexer structure 103 can have a width of 10 μm and a length of 110 μm in the waveguide direction. Furthermore, the multimode interferometric optical multiplexer / demultiplexer can be configured as a 3 dB coupler that splits the input light intensity into two by setting the output port positions on the first modulated optical waveguide 102a and the second modulated optical waveguide 102b at positions offset by ±2.5 μm from the center in the width direction of the multimode interferometric optical multiplexer / demultiplexer.

[0025] Furthermore, reflective sections 104 are provided at the ends of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b. The reflective sections 104 can be made of a highly reflective coating film with a reflectivity of 90% or more. In addition, an anti-reflective coating 105 can be provided at the end face (output end) of the laser section 101. The anti-reflective coating 105 can be made of a non-reflective coating film with a reflectivity of almost 0%.

[0026] The optical output from the laser unit 101 is split into a first modulated optical waveguide 102a and a second modulated optical waveguide 102b by the multiplexing / demultiplexing structure 103, propagates through the first modulated optical waveguide 102a and the second modulated optical waveguide 102b, and is modulated in each. The light that has propagated through the first modulated optical waveguide 102a and the second modulated optical waveguide 102b is reflected by the reflector 104 on the end face of the element, input to the multiplexing / demultiplexing structure 103, and returned to the optical waveguide by the active layer of the laser unit 101. The multiplexing / demultiplexing structure 103, the first modulated optical waveguide 102a, the second modulated optical waveguide 102b, and the reflector 104 constitute a reflective Mach-Zehnder modulator with a common input / output port.

[0027] Furthermore, the first modulated optical waveguide 102a and the second modulated optical waveguide 102b are configured to have the same length and the same propagation constant.

[0028] When the voltages applied to the second electrode 112a and the third electrode 112b are configured to be the same value but with different signs in a push-pull (operating) configuration, and the propagation constant of the first modulated optical waveguide 102a changes by Δβ, and the propagation constant of the second modulated optical waveguide 102b changes by -Δβ, the normalized optical losses in these regions are as shown in Figure 3. In Figure 3, L is twice the length of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b (round trip length).

[0029] By controlling the voltage amplitude applied to the second electrode 112a and the third electrode 112b, and thereby controlling the refractive index in the region where the voltage is applied, the loss of the Mach-Zehnder modulator with the above-mentioned input / output port in common can be controlled, and the internal loss of the resonator of the mixed-modulation laser 100 can be controlled.

[0030] Furthermore, as shown in Figure 3, it can be seen that by performing a push-pull operation with the same voltage amplitude, feedback can be performed without changing the phase of the light returned to the laser unit 101. In addition, by setting the applied voltage amplitude to a different value during the push-pull operation and setting the propagation constant of the first modulated optical waveguide 102a to β u The propagation constant of the phase control optical waveguide of the second modulated optical waveguide 102b is changed by =β+(1+δ)·Δβ / 2. l By changing the value by =β-(1-δ)·Δβ / 2, the phase of the light returned to the laser unit 101 can be controlled (Figure 4). Note that δ is an asymmetric parameter. This control allowed the feedback light phase to be set to the optimal condition for operating the mixed-modulation laser 100, and the frequency fluctuations of the output modulated light were controlled.

[0031] Figure 5 shows the frequency response characteristics of the mixed-modulation laser 100. By simultaneously applying electrical signals to the first electrode 111, the second electrode 112a, and the third electrode 112b, simultaneous modulation of the injection current to the laser unit 101 and loss modulation of the reflective Mach-Zehnder modulator by modulating the refractive indices of the first modulating optical waveguide 102a and the second modulating optical waveguide 102b are achieved. Reflecting the total element length of 410 μm, a second sensitivity improvement peak due to the photon resonance effect was observed near 120 GHz, confirming that the mixed-modulation laser 100 is a semiconductor laser light source with a bandwidth of 140 GHz or higher.

[0032] Figure 6 shows the output optical eye waveform when a large-amplitude 100 Gb / s NRZ (non-return-to-zero) signal is applied as a modulation signal to the first electrode 111, the second electrode 112a, and the third electrode 112b. As shown in Figure 6, the mixed-modulation laser 100 was able to obtain a good eye waveform with an extinction ratio of 3 dB or more at the central eye aperture.

[0033] Incidentally, the diffraction grating 121 of the laser unit 101 can be a phase-shift type diffraction grating. It goes without saying that the same characteristics as described above can be obtained by controlling the amount of phase shift and the phase shift position as a phase-shift type diffraction grating. Furthermore, although the above description showed a structure based on the electro-optic (Pockels) effect for refractive index control of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b, it goes without saying that the same effect can be obtained by introducing a structure that enables current injection, thereby allowing refractive index control by the carrier plasma effect.

[0034] Furthermore, while the above description described a structure in which the laser unit 101 and the wave-combining / decompressing structure 103 are directly coupled, it goes without saying that the same effect can be obtained by coupling the two with an optical waveguide. Also, while the above description described an operation in which the Δβ of the first modulated optical waveguide 102a is positive and the Δβ of the second modulated optical waveguide 102b is negative, it goes without saying that the opposite operation is also possible.

[0035] [Embodiment 2] Next, a mixed-modulation laser 100a according to Embodiment 2 of the present invention will be described with reference to Figure 7. The mixed-modulation laser 100a comprises a laser unit 101, a first modulating optical waveguide 102a, a second modulating optical waveguide 102b, and a multiplexing / demultiplexing structure 103a. The laser unit 101, the first modulating optical waveguide 102a, the second modulating optical waveguide 102b, and the multiplexing / demultiplexing structure 103a can be monolithically integrated on the same substrate.

[0036] The laser unit 101, the first modulated optical waveguide 102a, and the second modulated optical waveguide 102b are the same as in Embodiment 1 described above. In Embodiment 2, the multiplexing / demultiplexing structure 103a is composed of a Y-branch optical waveguide (Y-branch optical waveguide type optical multiplexer / demultiplexer). The multiplexing / demultiplexing structure 103a is a 3dB coupler structure that enables the optical output from the laser unit 101 to be equally distributed to the first modulated optical waveguide 102a and the second modulated optical waveguide 102b. For example, the length in the waveguide direction of the Y-branch optical waveguide constituting the multiplexing / demultiplexing structure 103a can be 120 μm, and the core width of the optical waveguide can be 1.5 μm.

[0037] The mixed-modulation laser 100a according to Embodiment 2 also obtained similar characteristics to the mixed-modulation laser 100 according to Embodiment 1, achieving good high-speed modulation operation characteristics, and the operation of the mixed-modulation laser 100a with a 100 Gb / s NRZ signal was confirmed.

[0038] [Embodiment 3] Next, a mixed-modulation laser 100b according to Embodiment 3 of the present invention will be described with reference to Figure 8. The mixed-modulation laser 100b comprises a laser unit 101, a first modulating optical waveguide 102a, a second modulating optical waveguide 102b, and a multiplexing / demultiplexing structure 103b. The laser unit 101, the first modulating optical waveguide 102a, the second modulating optical waveguide 102b, and the multiplexing / demultiplexing structure 103b can be monolithically integrated on the same substrate.

[0039] The laser unit 101, the first modulated optical waveguide 102a, and the second modulated optical waveguide 102b are the same as in Embodiment 1 described above. In Embodiment 3, the multiplexing / demultiplexing structure 103b is composed of a directional coupler (directional coupler structure optical multiplexing / demultiplexing). The multiplexing / demultiplexing structure 103b is a 3dB coupler structure that enables the optical output from the laser unit 101 to be equally distributed to the first modulated optical waveguide 102a and the second modulated optical waveguide 102b. For example, in the directional coupler that constitutes the multiplexing / demultiplexing structure 103b, the core width of the optical waveguide can be set to 1.5 μm, the waveguide spacing (core spacing) to 1 μm, and the waveguide direction length of the coupler portion to 140 μm.

[0040] In the mixed-modulation laser 100b, if the propagation constants of the first modulated optical waveguide 102a and the second modulated optical waveguide 102b are matched, the feedback light from the reflective Mach-Zehnder modulator structure will couple to one of the optical waveguides of the directional coupler constituting the multiplexing / demultiplexing structure 103b. For this reason, it is important to set the initial propagation constant difference between the first modulated optical waveguide 102a and the second modulated optical waveguide 102b to ΔβL = π.

[0041] Furthermore, during modulation in the first modulating optical waveguide 102a and the second modulating optical waveguide 102b, the optical components that become lost are coupled to one of the optical waveguides of the directional coupler constituting the multiplexing / demultiplexing structure 103b, and it is necessary to extract this to the outside in a non-reflective state. For this reason, an optical output waveguide 106, which has an oblique structure in plan view, is connected to one of the optical waveguides of the directional coupler constituting the multiplexing / demultiplexing structure 103b. The optical output waveguide 106 is terminated at the element end face parallel to the waveguide direction of the mixed-modulation laser 100b.

[0042] By setting the incidence angle of the optical emission waveguide 106 to 7° on the element end face of the mixed-modulation laser 100b, the residual reflectance is increased to 10 -4This was reduced to a certain extent. Furthermore, by providing an anti-reflective coating on the output end face of the optical output waveguide 106, further reduction in reflectivity is possible. By using the optical output waveguide 106 with an anti-reflective coating on the output end face, the optical components lost in the first modulated optical waveguide 102a and the second modulated optical waveguide 102b can be extracted to the outside without reflection at the output surface. As a result, the components mixed into the laser unit 101 were successfully reduced sufficiently, good high-speed modulation operation characteristics were achieved, and the operation of the mixed-modulation laser 100b with a 100 Gb / s NRZ signal was confirmed.

[0043] As described above, according to the present invention, the optical output from the laser unit is split into a first modulated optical waveguide and a second modulated optical waveguide, and the optical output from the first modulated optical waveguide to the laser unit and the optical output from the second modulated optical waveguide to the laser unit are combined, thereby suppressing frequency fluctuations in the output modulated light and making it easier to optimize the frequency response characteristics.

[0044] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art. [Explanation of Symbols]

[0045] 100... Mixed-modulation laser, 101... Laser section, 102a... First modulated optical waveguide, 102b... Second modulated optical waveguide, 103... Multiplexing and demultiplexing structure, 104... Reflecting section, 105... Anti-reflective coating, 111... First electrode, 112a... Second electrode, 112b... Third electrode, 121... Diffraction grating.

Claims

1. A laser section consisting of a distributed feedback laser equipped with an optical waveguide structure, A first modulated optical waveguide in which the optical loss and refractive index are modulated by the modulation of the injected current, A second modulated optical waveguide in which the optical loss and refractive index are modulated by the modulation of the injected current, A wave-splitting structure that splits the optical output from the laser unit into the first modulated optical waveguide and the second modulated optical waveguide, and combines the optical output from the first modulated optical waveguide to the laser unit and the optical output from the second modulated optical waveguide to the laser unit, Reflectors provided at the ends of the first modulated optical waveguide and the second modulated optical waveguide A mixed-modulation laser equipped with the following features.

2. In the mixed-modulation laser according to claim 1, The aforementioned multiplexing and demultiplexing structure is a mixed-modulation laser composed of a multimode interferometric photomultiplexer and demultiplexer.

3. In the mixed-modulation laser according to claim 1, The aforementioned wave-combining and decompressing structure is a mixed-modulation laser composed of a Y-branch optical waveguide.

4. In the mixed-modulation laser according to claim 1, The aforementioned wave-combining / decompressing structure is a mixed-modulation laser composed of a directional coupler.

Images